Particularly the way coleslaw is presented in the US. You can make a perfectly delicious and healthful coleslaw without mayonnaise or cream (or sugar!)

I just looked at the ingredients of a premade coleslaw (Safeway). The second and third ingredients are mayonnaise and sugar respectively.

Mayo in the US is poison, you couldn't pay me to eat it.

I think it's the rise of transported from afar cheap vegetables. Since they are more sturdy, they are cheaper, it's more lucrative (and budget friendly when cooking at home) to get bland supermarket tomatoes and make a salad with them, by adding sauce.

Locally sourced vegetables can be much more flavourful, reducing the need for additional sauces. I always enjoy making a "tomato, cucumber, olive oil" salad and watch foreigners coming to Bulgaria ask "oh wow what sauce did you use" and I go - none, that's how those veggies are supposed to taste.

But you only get those kind of supplies by going to a bazaar/market and pick them out individually yourself.